N.H. Al-Hardan

High Sensitivity pH Sensor Based on Porous Silicon (PSi) Extended Gate Field-Effect Transistor

In this study, porous silicon (PSi) was prepared and tested as an extended gate field-effect transistor (EGFET) for pH sensing. The prepared PSi has pore sizes in the range of 500 to 750 nm with a depth of approximately 42 µm. The results of testing PSi for hydrogen ion sensing in different pH buffer solutions reveal that the PSi has a sensitivity value of 66 mV/pH that is considered a super Nernstian value. The sensor considers stability to be in the pH range of 2 to 12. The hysteresis values of the prepared PSi sensor were approximately 8.2 and 10.5 mV in the low and high pH loop, respectively. The result of this study reveals a promising application of PSi in the field for detecting hydrogen ions in different solutions.

Temperature-Driven Structural and Morphological Evolution of Zinc Oxide Nano-Coalesced Microstructures and Its Defect-Related Photoluminescence Properties

In this paper, we address the synthesis of nano-coalesced microstructured zinc oxide thin films via a simple thermal evaporation process. The role of synthesis temperature on the structural, morphological, and optical properties of the prepared zinc oxide samples was deeply investigated. The obtained photoluminescence and X-ray photoelectron spectroscopy outcomes will be used to discuss the surface structure defects of the prepared samples. The results indicated that the prepared samples are polycrystalline in nature, and the sample prepared at 700 °C revealed a tremendously c-axis oriented zinc oxide. The temperature-driven morphological evolution of the zinc oxide nano-coalesced microstructures was perceived, resulting in transformation of quasi-mountain chain-like to pyramidal textured zinc oxide with increasing the synthesis temperature. The results also impart that the sample prepared at 500 °C shows a higher percentage of the zinc interstitial and oxygen vacancies. Furthermore, the intensity of the photoluminescence emission in the ultraviolet region was enhanced as the heating temperature increased from 500 °C to 700 °C. Lastly, the growth mechanism of the zinc oxide nano-coalesced microstructures is discussed according to the reaction conditions.

Amperometric Non-Enzymatic Hydrogen Peroxide Sensor Based on Aligned Zinc Oxide Nanorods

Zinc oxide (ZnO) nanorods (NRs) have been synthesized via the hydrothermal process. The NRs were grown over a conductive glass substrate. A non-enzymatic electrochemical sensor for hydrogen peroxide (H2O2), based on the prepared ZnO NRs, was examined through the use of current-voltage measurements. The measured currents, as a function of H2O2 concentrations ranging from 10 μM to 700 μM, revealed two distinct behaviours and good performance, with a lower detection limit (LOD) of 42 μM for the low range of H2O2 concentrations (first region), and a LOD of 143.5 μM for the higher range of H2O2 concentrations (second region). The prepared ZnO NRs show excellent electrocatalytic activity. This enables a measurable and stable output current. The results were correlated with the oxidation process of the H2O2 and revealed a good performance for the ZnO NR non-enzymatic H2O2 sensor.

A Study on the UV Photoresponse of Hydrothermally Grown Zinc Oxide Nanorods With Different Aspect Ratios

We report on the effect of the aspect ratio of zinc oxide (ZnO) nanorods (NRs) prepared by the hydrothermal process. It was found that increasing the precursor molar amount resulted in the decrease of the aspect ratio of ZnO NRs. Furthermore, the aspect ratios showed a significant effect on the structural and optical properties of the prepared ZnO NRs. The ZnO NRs were fabricated into a metal-semiconductor-metal (MSM) UV photodetector. The performances of the prepared MSM ZnO NRs were also studied, and the high aspect ratio showed that the highest responsivity had a value of 33 A/W at a bias voltage of 5 V and a wavelength of 380 nm. The responsivity, rise time, and full time of the prepared ZnO NRs showed a trend of behavior as the molar amount of the precursor was varied.

Surface and interface phonon polariton characteristics of wurtzite ZnO/GaN heterostructure

Surface and interface phonon polariton modes in wurtzite ZnO/GaN heterostructure on wurtzite 6H–SiC substrate were investigated by a variable angle p-polarized infrared attenuated total reflection spectroscopy. Three dips corresponding to the surface and interface phonon polariton modes were observed; two of the dips that having a lower intensity level of reflectivity were the leaky modes whereas, another one was a real mode. The observations were verified with the surface polariton dispersion curve simulated based on an anisotropy model for a four-layer system. It was shown that the frequencies of leaky modes are predictable by considering the damping of the substrate.Surface and interface phonon polariton modes in wurtzite ZnO/GaN heterostructure on wurtzite 6H–SiC substrate were investigated by a variable angle p-polarized infrared attenuated total reflection spectroscopy. Three dips corresponding to the surface and interface phonon polariton modes were observed; two of the dips that having a lower intensity level of reflectivity were the leaky modes whereas, another one was a real mode. The observations were verified with the surface polariton dispersion curve simulated based on an anisotropy model for a four-layer system. It was shown that the frequencies of leaky modes are predictable by considering the damping of the substrate.

Optical Analysis of Nanocrystalline ZnO Films Coated on Porous Silicon by Radio Frequency (RF) Magnetron Sputtering

Zinc oxide thin films have been deposited onto porous silicon (PSi) substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The advantages of the porous Si template are economical and it provides a rigid structural material. Porous silicon is applied as an intermediate layer between silicon and ZnO films and it contributed a large area composed of an array of voids. The nanoporous silicon samples were adapted by photo electrochemical (PEC) etching technique on n-type silicon wafer with (111) and (100) orientation. Micro-Raman and photoluminescence (PL) spectroscopy are powerful and non-destructive optical tools to study vibrational and optical properties of ZnO nanostructures. Both the Raman and PL measurements were also operated at room temperature. Micro-Raman results showed that the A1(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at around 522 and 530 cm–1, re- spectively. PL spectra peaks are distinctly apparent at 366 and 368 cm–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The peak luminescence energy in nanocrystalline ZnO on porous silicon is blue-shifted with regard to that in bulk ZnO (381 nm). The Raman and PL spectra pointed to oxygen vacancies or Zn interstitials which are responsible for the green emission in the nanocrystalline ZnO.

Effect of low H2 concentrations on the current-voltage characteristic of ZnO gas sensor

Abstract Abstract A self-heated ZnO gas sensor was prepared through thermal oxidation of Zn metal for 30 and 60 min in oxygen atmosphere. The XRD results confirmed the conversion of Zn metal to ZnO. The current-voltage measurements showed changes in forward current in the presence of hydrogen gas, with the concentration ranging from 40 to 160 ppm. A better resolution of current response due to H2 concentrations was obtained for the samples with 30 min oxidation, although both samples showed enhanced response with the applied voltage. The barrier height of both samples was found to decrease with H2 concentrations, thus aiding in the increase in current response.

Electrochemical Hydrogen Peroxide Sensor Based on Macroporous Silicon

Macroporous silicon was prepared through an anodization process; the prepared samples showed an average pore size ranging from 4 to 6 microns, and the depth of the pores in the silicon wafer was approximately 80 microns. The prepared samples were tested for hydrogen peroxide (H2O2) concentrations, which can be used for industrial and environmental sensing applications. The selected H2O2 concentration covered a wide range from 10 to 5000 μM. The tested samples showed a linear response through the tested H2O2 concentrations with a sensitivity of 0.55 μA μM–1∙cm–2 and lower detection limits of 4.35 μM at an operating voltage of 5 V. Furthermore, the electrode exhibited a rapid response with a response time of ca. two seconds. Furthermore, the prepared sensor showed a reasonable stability over a one-month time period.

Ultraviolet Sensors Based on Two-Dimensional Zinc Oxide Structures

In this chapter, we review the application of zinc oxide (ZnO) in ultraviolet (UV) sensing and emphasise on the two-dimensional (2D) ZnO structures. The synthesis of 2D ZnO structures, the morphologies, and the photoluminescence emission will be reviewed and highlighted. The performance of the UV sensors based on 2D ZnO structures is explored. The lack in the study of the 2D ZnO UV sensors might be due to the difficulties of controlling the growth of the 2D ZnO compared to the one-dimensional (1D) ZnO structures.

Synthesis and Characterization of Grape-Like SnO2 Structures Grown by a Thermal Evaporation Method

Grape-like tin dioxide (SnO2) structures have been grown on p-type silicon (Si(100)) substrate synthesized by thermal evaporation of tin (Sn) without use of metal catalyst. The experiment were conducted in a three-zone tube furnace at a constant temperature of 1080°C,under 1.6% of oxygen (O2) gas in an atmospheric ambient with a controlled flow rate of 1.0L/min. The prepared SnO2 film was characterized by using X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy(EDX) and photoluminescence (PL) measurement. The grape-like SnO2 structures were highly crystalline with particle size (resemble grape fruit) ranging from 120-550 nm and diameter of wire (resemble grape stem) around 120-160 nm.The PL spectrum of the grape-like SnO2 structures exhibits a broad visible light emission with a peak centered at around 623 nm, corresponding to 1.99 eV and usual near band edge emission of SnO2 is not observed.